Prior to the 14th century, when the pendulum clock was invented, the sundial was the primary means for measuring time. Many varieties are still in use today, often more for decorative than functional purposes.
Generally, sundials use a style or gnomon arranged to cast a shadow on a time scale. The invention of the shadowless sundial is described in U.S. Pat. No. 3,815,249, and is based on the use of reflection highlights producing images of the sun. Time is marked by the changing position of these images relative to a fixed time scale. Because it requires no sharp pointer, or gnomon, to cast a shadow, and in fact can be used under a hazy sun that casts no discernable shadow, advantages of safety, attractivness, economy, ease of adjustment, accuracy, reliability, and enhanced usefulness are realized. One disadvantage of shadowless sundials disclosed in said patent, however, has been the need for a means to sight the reflection image of the sun from a point located precisely on the axis of revolution of the sundial. Except for very large embodiments, such as monuments, it is necessary to read the time with one eye closed to avoid parallax.